1. Field of the Invention
This invention relates to a wiper apparatus used for wiping a wiping surface of, for example, a windshield of a motor vehicle with a wiper blade and, more particularly to the wiper apparatus which works interlockingly with operation of a washer to spray cleaning liquid against the wiping surface.
2. Description of the Prior Art
Heretofore, there has been used a wiper apparatus interlocking to a washer shown in FIG. 3, for example.
An illustrated wiper apparatus 100 is provided with a washer switch 101 for actuating a washer motor (not shown) and spraying cleaning liquid toward a wiping surface 50, and a relay 102, which is so structured as to be switched on interlockingly to on-operation of the washer switch 101 and switched off at the end of a time period set by timer (not shown) housed in a drive circuit 104 after the washer switch 101 is turned off.
A traveling contact 102a of the relay 102 is connected to an power terminal 103a provided to a wiper motor 103, and another power terminal 103b of the wiper motor 103 is connected to the drive circuit 104 provided with the timer.
An output shaft 103c of the wiper motor 103 is connected to a base end of a wiper arm 106 disposed rotatably on a vehicle body 60 through a wiper linkage 105.
A wiper blade 107 is fitted to a top end of the wiper arm 106, the wiper blade 107 is pushed against the wiping surface 50 by tensile force of a spring (not shown) housed in the wiper arm 106.
Upon rotating the output shaft 103c by actuating the wiper motor 103, the rotation of the output shaft 103c is converted into reciprocating motion of the wiper arm 106 through the wiper linkage 105, and the wiping surface 50 is wiped with the wiper blade 7 between both turning positions A and B.
On the other side, the wiper motor 103 is provided with an autostop switch 103d to stop the wiper blade 107 at a stop position (turning position B), and the autostop switch 103d is provided with an inner conductive plate 103e grounded and an outer conductive plate 103f, which are so constructed as to be rotatably linked with the output shaft 103c.
The autostop switch 103d is provided with an autostop contact 103g to come in or off contact with the inner conductive plate 103e and the outer conductive plate 103f, and another autostop contact 103h to come in or off contact with the outer conductive plate 103f, and the autostop contact 103g is connected with an off-contact 102b of the relay 102.
Another autostop contact 103h is connected to a power source, and an on-contact 102c of the relay 102 is grounded.
Spraying the cleaning liquid by turning the washer switch 101 on, the traveling contact 102a of the relay 102 is switched to the on-contact 102c from the off-contact 102b and comes in contact with the on-contact 102c, thereby the power terminal 103a of the wiper motor 103 is grounded and an electric current is supplied to the power terminal 103a from another power terminal 103b of the wiper motor 103 through the drive circuit 104.
The wiper motor 103 works and the wiping surface 50 is wiped with the wiper blade 107 between both turning positions A and B according to the rotation of the output shaft 103c of the wiper motor 103.
In this state, even if the spray of the cleaning liquid is stopped by switching off the washer switch 101, the wiper motor 103 does not stop immediately and continues to rotate as long as a predetermined time period by the function of the timer provided in the drive circuit 104. The traveling contact 102a of the relay 102 shifts to the off-contact 102b from the on-contact 102c when the predetermined time set by the timer elapses after the off-operation of the washer switch 101.
When the traveling contact 102a of the relay 102 comes in contact with the off-contact 102b, the wiper motor 103 continues to rotate for a while because the power terminal 103a of the wiper motor 103 is grounded through the autostop contact 103g and the inner conductive plate 103e if the wiper blade 107 is not in the turning position B. When the wiper blade 107 arrives at the turning position B by the rotation of the wiper motor 103, the autostop contact 103g of the autostop switch 103d separates from the inner conductive plate 103e and comes in contact with the outer conductive plate 103f. At the same time another autostop contact 103h comes also in contact with the outer conductive plate 103f.
Thereby, the power terminal 103a of the wiper motor 103 is connected to the power source through the outer conductive plate 103f, and the voltage applied to the power terminal 103a becomes equal to the voltage applied to another power terminal 103b of the wiper motor 103 so that the wiper motor 103 stops automatically with the wiper blade 107 remaining in the turning position B.
In addition to above, the wiper apparatus 100 is also provided with a wiper switch (not shown) for actuating the wiper motor 103 independently of the operation of the washer switch 101.
However, the aforementioned conventional wiper apparatus 100 is so structured that the wiper motor 103 continues to rotate merely for a time period set by the timer in the drive circuit 104 after the off-operation of the washer switch 101, and the time period set by the timer is constant. Therefore, the wiper blade 107 may stop wiping the wiping surface 50 in spite of the fact that the cleaning liquid is not yet wiped away from the wiping surface 50, and this is a problem since the cleaning liquid remaining on the wiping surface 50 obstructs the visual range of the driver in such a case.